This application is a divisional of U.S. patent application Ser. No. 10/403,539, filed Mar. 31, 2003 now U.S. Pat. No. 6,766,136 (now allowed), which is a divisional of U.S. patent application Ser. No. 09/747,764, filed Dec. 26, 2000, now U.S. Pat. No. 6,610,451 B2 which is incorporated herein in its entirety by reference.
The present invention relates to magnetic toners and development systems for magnetic toners.
Magnetic ink character recognition (MICR) printing has been used for many years for checks and negotiable documents as well as for other documents in need of high speed reading and sorting. Various electrophotographic printers which are capable of printing magnetic inks or toners have been available from such sources as IBM and Kodak. Typically, the toner or ink used for MICR applications contains a heavy loading of iron oxide or other magnetic material in order to obtain the required adequate magnetic signal strength for speed reading and sorting and the like. However, MICR toner having such heavy iron oxide loadings can be quite difficult to manufacture since an adequate dispersion of the iron oxide particles in the toner resin, for instance, is hard to achieve and maintain. Furthermore, the resulting image quality from the MICR toner can be degraded relative to images made with normal toner due to decreased toning and fusing efficiencies resulting from the magnetic loadings that are required in the toner.
Accordingly, there is a significant trade off that currently occurs in the MICR technology; namely, a significant amount of magnetic loadings are required in order to achieve the necessary magnetic signal strength and yet this same magnetic loading leads to degraded images or images that have low quality. In order to obtain a higher image quality, the magnetic loading would need to be reduced which would then jeopardize the necessary magnetic signal strength that is required. Accordingly, the industry has simply accepted the lower quality of image in view of the need for the adequate magnetic signal strength that must be present in the MICR toner. Currently, MICR toners in the industry range in iron oxide loadings of up to and even above 50% by weight of the toner. With a loading of over 28% by weight Fe3O4 in a conventional MICR developer for an IBM 3828 MICR printer (2 component developer using a soft magnetic carrier), the signal strength for the release toner is between 120% and 140% average signal strength of the “on-us” characters as measured on a DOCU-MATE Check Reader. This 120% signal strength is sufficient and required to compensate for character voids and otherwise low density individual image. However, as indicated above, using such a toner, no matter what currently available printer or development system is used, typically leads to image quality which is at best mediocre.
The present invention may be more fully understood with reference to the accompanying figures. The figures are intended to illustrate exemplary embodiments of the present invention without limiting the scope of the invention. The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the present invention and together with the description, serve to explain the principles of the present invention.